Unlike its predecessor, Windows Server 2012 has no support for Itanium-based computers,[6] and has four editions. Various features were added or improved over Windows Server 2008 R2 (with many placing an emphasis on cloud computing), such as an updated version of Hyper-V, an IP address management role, a new version of Windows Task Manager, and ReFS, a new file system. Windows Server 2012 received generally good reviews in spite of having included the same controversial Metro-based user interface seen in Windows 8.

The successor to Windows Server 2012, called Windows Server 2012 R2, was released along with Windows 8.1 in October 2013. A service pack, formally designated Windows Server 2012 R2 Update, was released in April 2014.[7][8]

Windows Server 2012, codenamed "Windows Server 8",[4] is the sixth release of Windows Server family of operating systems developed concurrently with Windows 8.[9][10] It was not until April 17, 2012 that the company announced that the final product name would be "Windows Server 2012".[4]

Microsoft introduced Windows Server 2012 and its developer preview in the BUILD 2011 conference on September 9, 2011.[11] However, unlike Windows 8, the developer preview of Windows Server 2012 was only made available to MSDN subscribers.[12] It included a graphical user interface (GUI) based on Metro design language and a new Server Manager, a graphical application used for server management.[13] On February 16, 2012, Microsoft released an update for developer preview build that extended its expiry date from April 8, 2012 to January 15, 2013.[14]

Before Windows Server 2012 was finalized, two test builds were made public. A public beta version of Windows Server 2012 was released along with the Windows 8 Consumer Preview on February 29, 2012.[9] The release candidate of Windows Server 2012 was released on May 31, 2012, along with the Windows 8 Release Preview.[10]

Unlike its predecessor, Windows Server 2012 can switch between "Server Core" and "Server with a GUI" installation options without a full reinstallation. Server Core - an option with a command-line interface only - is now the recommended configuration. There is also a third installation option that allows some GUI elements such as MMC and Server Manager to run, but without the normal desktop, shell or default programs like File Explorer.[13]

Server Manager has been redesigned with an emphasis on easing management of multiple servers.[18] The operating system, like Windows 8, uses the Metro-based user interface unless installed in Server Core mode.[19]Windows Store is available in this version of Windows but is not installed by default.[20]Windows PowerShell in this version has over 2300 commandlets, compared to around 200 in Windows Server 2008 R2.[21]

Windows Server 2012 includes a new version of Windows Task Manager together with the old version.[22] In the new version the tabs are hidden by default showing applications only. In the new Processes tab, the processes are displayed in varying shades of yellow, with darker shades representing heavier resource use.[23] It lists application names and status, as well as CPU, memory, hard disk and network utilization. The process information found in the older versions are now moved to the new Details tab. The Performance tab shows "CPU", "Memory", "Disk", "Wi-Fi" and "Ethernet" graphs. The CPU tab no longer displays individual graphs for every logical processor on the system by default; instead, it can display data for each non-uniform memory access (NUMA) node. When displaying data for each logical processor for machines with more than 64 logical processors, the CPU tab now displays simple utilization percentages on heat-mapping tiles.[24] The color used for these heat maps is blue, with darker shades again indicating heavier utilization. Hovering the cursor over any logical processor's data now shows the NUMA node of that processor and its ID, if applicable. Additionally, a new Startup tab has been added that lists startup applications,[25] however this tab does not exist in Windows Server 2012.[26] The new task manager recognizes when a Windows Store app has the "Suspended" status.

Windows Server 2012 has a number of changes to Active Directory from the version shipped with Windows Server 2008 R2. The Active Directory Domain Services installation wizard has been replaced by a new section in Server Manager, and a GUI has been added to the Active Directory Recycle Bin.[28] Multiple password policies can be set in the same domain.[29] Active Directory in Windows Server 2012 is now aware of any changes resulting from virtualization, and virtualized domain controllers can be safely cloned. Upgrades of the domain functional level to Windows Server 2012 are simplified; it can be performed entirely in Server Manager. Active Directory Federation Services is no longer required to be downloaded when installed as a role, and claims which can be used by the Active Directory Federation Services have been introduced into the Kerberos token. Windows Powershell commands used by Active Directory Administrative Center can be viewed in a "Powershell History Viewer".[30][31]

Windows Server 2012, along with Windows 8, includes a new version of Hyper-V,[32] as presented at the Microsoft BUILD event.[33] Many new features have been added to Hyper-V, including network virtualization, multi-tenancy, storage resource pools, cross-premise connectivity, and cloud backup. Additionally, many of the former restrictions on resource consumption have been greatly lifted. Each virtual machine in this version of Hyper-V can access up to 64 virtual processors, up to 1 terabyte of memory, and up to 64 terabytes of virtual disk space per virtual hard disk (using a new .vhdx format).[34][35] Up to 1024 virtual machines can be active per host, and up to 8000 can be active per failover cluster.[36]SLAT is a required processor feature for Hyper-V on Windows 8, while for Windows Server 2012 it is only required for the supplementary RemoteFX role.[37]

Resilient File System (ReFS),[38] codenamed "Protogon",[39] is a new file system in Windows Server 2012 initially intended for file servers that improves on NTFS in some respects. Major new features of ReFS include:[40][41]

Improved reliability for on-disk structures

ReFS uses B+ trees[40] for all on-disk structures including metadata and file data. Metadata and file data are organized into tables similar to a relational database. The file size, number of files in a folder, total volume size and number of folders in a volume are limited by 64-bit numbers; as a result ReFS supports a maximum file size of 16 Exabytes, a maximum of 18.4 × 1018 folders and a maximum volume size of 1 Yottabyte (with 64 KB clusters) which allows large scalability with no practical limits on file and folder size (hardware restrictions still apply). Free space is counted by a hierarchical allocator which includes three separate tables for large, medium, and small chunks. File names and file paths are each limited to a 32 KB Unicode text string.

Built-in resilience

ReFS employs an allocation-on-write update strategy for metadata,[40] which allocates new chunks for every update transaction and uses large IO batches. All ReFS metadata has built-in 64-bit checksums which are stored independently. The file data can have an optional checksum in a separate "integrity stream", in which case the file update strategy also implements allocation-on-write; this is controlled by a new "integrity" attribute applicable to both files and directories. If nevertheless file data or metadata becomes corrupt, the file can be deleted without taking the whole volume offline. As a result of built-in resiliency, administrators do not need to periodically run error-checking tools such as CHKDSK when using ReFS.

Reviews of Windows Server 2012 have been generally positive.[56][57][58] Simon Bisson of ZDnet described it as "ready for the datacenter, today,"[56] while Tim Anderson of The Register said that "The move towards greater modularity, stronger automation and improved virtualisation makes perfect sense in a world of public and private clouds" but remarked that "That said, the capability of Windows to deliver obscure and time-consuming errors is unchanged" and concluded that "Nevertheless, this is a strong upgrade overall."[57]InfoWorld noted that Windows Server 2012 has the Metro UI, which had led to mixed reviews for Windows 8, but mentioned that "Microsoft is pushing harder for a GUI-less install than a Metro-based screen", with reference to the improved Server Core installation option and the improvements for Windows PowerShell.[59] However, Michael Otey of Windows IT Pro expressed dislike with the new Metro interface and the lack of ability to use the older desktop interface alone, saying that most users of Windows Server manage their servers using the graphical user interface rather than PowerShell.[60] The Australian construction company Kennards found the OS stable.[61]

Paul Ferrill wrote that "Windows Server 2012 Essentials provides all the pieces necessary to provide centralized file storage, client backups, and remote access,"[62] but Tim Anderson contended that "Many businesses that are using SBS2011 and earlier will want to stick with what they have", citing the absence of Exchange, the lack of ability to synchronize with Active Directory Federation Services and the 25-user limit,[63] while Paul Thurott wrote "you should choose Foundation only if you have at least some in-company IT staff and/or are comfortable outsourcing management to a Microsoft partner or solution provider" and "Essentials is, in my mind, ideal for any modern startup of just a few people."[64]

Windows Server 2012 R2 was released on October 18, 2013.[65] It was unveiled on June 3, 2013 at TechEd North America.[66] According to Windows Server 2012 R2 datasheet published on May 31, 2013, there are four editions of this operating system: Foundation, Essentials, Standard and Datacenter.[67] As with Windows Server 2012, the Datacenter and Standard editions are feature identical, varying only based on licensing (particularly licensing of virtual instances). The Essentials edition has the same features as the Datacenter and Standard products, with some restrictions.[68]

A further update, formally designated Windows Server 2012 R2 Update, was released in April 2014.[7]

Internet Information Services 8.5: Support for logging to Event Tracing for Windows and the ability to log any request/response headers. To improve scalability, if IIS is configured with 100 or more web sites, by default it will not automatically start any of them. Alongside this, a new "Idle Worker Process Page-Out" configuration option has been added to application pools to instruct Windows to page-out the process if it has been idle for the idle time-out period (by default, 20 minutes).[72]

Group Policy has a new "Policy Cache" setting which allows domain-joined machines to store a copy of the group policy settings on the client machine and, depending on the speed of access to the domain controller, use those at startup time instead of waiting for the policy settings to download. This can improve startup times on machines that are disconnected from the company network.[77] New Group Policy settings have been added to cover new features in Windows 8.1 and Internet Explorer 11, such as enabling/disabling SPDY/3 support, configuring start screen layouts, and detecting phone numbers in web pages.[78]

TLS support is extended to support RFC 5077, "Transport Layer Security (TLS) Session Resumption without Server-Side State", which improves performance of long-running TLS-secured connections that need to reconnect due to session expiration.

^Each virtualized partition, including the host itself, can use up to 64 processors.[49]

^ abcEach license of Windows Server 2012 Standard or Datacenter allows up to two processor chips. Each license of Windows Server 2012 Standard allows up to two virtual instances of Windows Server 2012 Standard on that physical server. If more virtual instances of Windows Server 2012 Standard are needed, each additional license of Windows Server 2012 allows up to two more virtual instances of Windows Server 2012 Standard, even though the physical server itself may have sufficient licenses for its processor chip count. Because Windows Server 2012 Datacenter has no limit on the number of virtual instances per licensed server, only enough licenses for the physical server are needed for any number of virtual instances of Windows Server 2012 Datacenter. If the number of processor chips or virtual instances is an odd number, the number of licenses required is the same as the next even number. For example, a single-processor-chip server would still require 1 license, the same as if the server were two-processor-chip and a five-processor-chip server would require 3 licenses, the same as if the server were six-processor-chip, and if 15 virtual instances of Windows Server 2012 Standard are needed on one server, 8 licenses of Windows Server 2012, which can cover up to 16 virtual instances, are needed (assuming, in this example, that the processor chip count does not exceed 16).

^ abFor the Standard and Datacenter editions, each user or device accessing the software must have a client access license (CAL) assigned (either per-user or per-device), so there may be no more simultaneous users than the number of client-access licenses, except up to 2 simultaneous users purely to administer the server software, or for running virtualization or web workloads. Remote Desktop Services requires an additional CAL separate from the aforementioned CAL.

^ abIf the number of physical processors in a particular server is under 64, the limit is determined by the quantity of licenses assigned to that server. In that case, the number of physical processors cannot exceed twice the number of licenses assigned to the server.